In the production of an air hose or oil hose for an automobile, nitrile rubber (abbreviated as "NBR" hereinafter) has been typically used for its inner tube and chloroprene rubber (abbreviated as "CR") for its outer tube (JP-A-H04-283255(1992)) since oil resistance is required for the inner tube and weather resistance for the outer tube, and in the case that heat resistance is specifically required, acrylic rubber (abbreviated as ACM), for example, has been used for the outer tube (JP-A-S64-14265(1989) and JP-A-H04-283255 (1992)).
Recently, pressure resistance enough to withstand the supercharger pressure as high as 0.15 MP is required in air hoses in use for supercharger in a vehicle equipped with a turbo charger for obtaining enhanced engine power and heat-aging resistance under rigorous conditions such as at operations of about 10,000 hours at 150.degree. C. is required for the inner tube materials, and, an attempt has been made to use fluorinated rubber (abbreviated as "FKM"), at least, for the inner tube of a heat-resistant hose (JP-A-H01-152060(1989)).
However, such rigorous heat-resistance requirements cannot be satisfied with the hoses using NBR for the inner tubes and CR for the outer tubes or with those hoses using ACM materials. Moreover, when fluid such as high temperature engine oil is to be transported, such hoses as described above are not able to provide both high level heat-resistance and oil resistance simultaneously.
On the other hand, there are problems with the heat-resistant hoses using FKM for, at least, its inner tubes that they are expensive and that FKM, when used for supercharger air hoses, will be deteriorated by amine components contained in engine oil as an additive since the turbo charger mechanism circulates a part of high temperature waste gas containing particles of engine oil into the air hose, and thus FKM hoses are also difficult to satisfy both high level heat-resistance and oil resistance simultaneously.
Heat-resistant hoses ordinarily contain fibers wound around between the inner and outer tubes for reinforcement purpose. Fiber reinforcements made by knitting filament threads with smooth surfaces have been conventionally used in many cases. However, since the bonding strength between the inner tube and such fiber reinforcements is not sufficient, when the hose is subjected to internal pressure change repeatedly, threads at the end of the hose may shrink toward the center of the hose due to changes in the hose diameters, causing slip-out of the threads, which will impair the air-tightness or liquid-tightness. Such defects or disadvantages tend to become more remarkable as requirements for heat-resistance become more rigorous.
Therefore, an object of the present invention is to solve these problems and provide a heat-resistant hose which is excellent in oil resistance, pressure resistance and heat-aging resistance and that is suitable for transport of fluid containing high temperature oil.